The 12 Query Types

https://baymard.com/blog/ecommerce-search-query-types

Good video on testing performance of elasticsearch

https://www.elastic.co/elasticon/conf/2018/sf/the-seven-deadly-sins-of-elasticsearch-benchmarking

Very good video about migration from the Amazon ES service to a self-managed cluster (with all concerns, reasons and hard decisions behind described well). Sometimes I had the feeling like that guy is telling my story.
https://www.elastic.co/elasticon/conf/2018/sf/lyfts-wild-ride-from-amazon-es-to-self-managed-elasticsearch

Some ideas on calculating trending things

https://stackoverflow.com/questions/787496/what-is-the-best-way-to-compute-trending-topics-or-tags/826509#826509

New book

New and promising search-related book was published on Manning Publications's MEAP - Deep Learning for Search

Use this free bayesian A/B testing calculator to find out if your test results are statistically significant.

Use this free bayesian A/B testing calculator to find out if your test results are statistically significant. 
https://marketing.dynamicyield.com/bayesian-calculator/

Learning to rank problems. Well explained

Learn to rank and its various optimizations - http://opensourceconnections.com/blog/2017/08/03/search-as-machine-learning-prob/

http://opensourceconnections.com/blog/2017/04/01/learning-to-rank-linear-models/